1. Technical Field
Exemplary aspects of the present invention generally relate to a driving force transmission unit to transmit a driving force to a target and an image forming apparatus including the driving force transmission unit, and more particularly to an image forming apparatus such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof.
2. Description of the Related Art
Generally, a driving force transmission unit includes a rotary body at a drive source side (hereinafter referred to as drive-source rotary body) and at least two connecting portions at which the drive-source rotary body and a rotary body at a rotation target side (hereinafter referred to as rotation-target rotary body) are connected, and the connecting portions are disposed on a transmission path through which the driving force from the drive source is transmitted to the rotation target such as a roller and a drum.
Examples of such connecting portions include a meshing portion at which two gears mesh with each other, a fitting portion on a rotary shaft to which a gear or a pulley is fitted, and a coupling (shaft coupling) that connects two rotary shafts at the shaft ends. At such connecting portions, rotation of the drive-source rotary body driven by the drive source causes a contact portion of the drive-source rotary body to push the rotation-target rotary body, thereby transmitting a rotary driving force to the rotation-target rotary body.
Generally, there are two or more connecting portions that connect the drive-source rotary body and the rotation-target rotary body. The connecting portions are generally provided with some play or backlash. Furthermore, manufacturing errors and meshing errors exist. As a result, not all the contact portions of the drive-source rotary body and the rotation-target rotary body are always in contact with each other, and the contact portions that come into contact change alternately.
As the contact portions that come into contact change, undesirable collision may occur between the contact portion of the drive-source rotary body and the contact portion of the rotation-target rotary body, generating vibration. If the vibration is significant, devices equipped with the driving force transmission unit may cause various problems. For example, the vibration in the driving force transmission unit in an image forming apparatus during image formation causes imaging failure, thereby producing an image defect.
In attempting to prevent undesirable vibration when there is an axis shift between a coupling of a drive shaft (i.e., the drive-source rotary body) and a coupling of a driven shaft (i.e., the rotation-target rotary body), in one approach, a known driving force transmission unit includes a plurality of claws on each of the drive shaft and the driven shaft. That is, the claws of the drive shaft contact the claws of the driven shaft at multiple places. Such a configuration is disclosed in Japanese Patent 4604063, for example.
At such couplings, the axis shift causes uneven contact between the claws of the drive shaft and the claws of the driven shaft, causing uneven transmission of the driving force at the contact portions. According to Japanese Patent 4604063, uneven transmission of the driving force causes transmission of the undesirable torque to the driven shaft. Furthermore, an excessive force acts in a certain direction on a plane perpendicular to the axis line. The direction of the excessive force is not constant, but varies while rotating, generating cyclic vibration. The driving force transmission unit in Japanese Patent 4604063 is to reduce the vibration when the axis shift exists at the couplings of the shafts.
In the known driving force transmission unit, the vibration that occurs at each of the contact portions is suppressed individually, thereby reducing the vibration of the driving force transmission unit as a whole. However, as described above, generally, there are more than two connecting portions at which the drive-source rotary body and the rotation-target rotary body are connected. When vibration at each of the plurality of the connecting portions is superimposed and amplified, significant vibration may occur. The vibration due to amplification of the vibrations at the plurality of the connecting portions tends to be greater than the individual vibration generated at each of the connecting portions. Thus, the devices equipped with such a driving force transmission unit cause more serious problems.
At the connecting portion, in particular, at the connecting portion using the couplings, the vibration due to the axis shift between the drive shaft and the driven shaft is greater than the vibration at other connecting portions. Therefore, reducing the vibration at the coupling is advantageous in terms of preventing various problems derived from the vibration generated in the drive power transmission unit. Although advantageous, even when the vibration is reduced at the coupling, if the reduced vibration is superimposed on the vibration generated at other connecting portions and amplified, greater vibration is generated, causing various problems.